Gas-filled electric discharge devices



April 21, 1964 B. o. BAKER ETAL GAS-FILLED ELECTRIC DISCHARGE DEVICESFiled Jan. 15, 1962 q-rToRNe'Ys 3,130,344 GAS-FILLED ELECTRIC DISCHARGEDEVICES .Basil Olior Baker, Croxley Green, and Robert Joseph Wheldon,Chaliont St. Peter, England, assignors to The M-O Valve Company Limited,London, England Filed Jan. 15, 1962, Ser. No. 166,283 Claims priority,application Great Britain Jan. 20, 1961 Claims. (Cl. 313-220) Thisinvention relates to gas-filled electric discharge devices.

It is an object of the present invention to provide a convenient form ofgas-filled electric discharge device of the kind having an envelopecomprising at least two metal parts arranged to be maintained atdifferent potentials in operation and insulated from one another bymeans of a ceramic portion which also forms part of the envelope of thedevice.

According tothe invention, a gas-filled electric discharge device has asealed gas-filled envelope including a hollow generally metallicstructure, an annular ceramic member sealed to said hollow structure anda metallic closure member sealed to the ceramic member so as to closethe aperture in the ceramic member, and the device has an electrodesystem including at least a cathode and an anode and disposed withinsaid hollow structure so that the main discharge path between theelectrodes of said system lies on the side of the anode remote from theceramic member, the anode being electrically connected to the closuremember and electrically insulated from said -with the length of theshortest path within the envelope between the closure member and saidhollow structure via the gas-filling.

One arrangement in accordance with the invention will now be described,by way of example, with reference to the accompanying drawing which is adiagrammatic sectional view of a thyratron having a peak inverse andforward hold-otf voltage rating of 40 kilovolts.

Referring to the drawing, the valve has a sealed, deuterium-filledenvelope which includes a copper portion including a relatively widetubular section 1 and relatively narrow tubular section 2 which iscoaxial with and extends beyond one end of the section 1. The sections 1and 2 are joined together by means of a copper flange 3 which is sealedto the inside of the section 1 and to the outsideof the section 2, oneface of the flange 3 being coplanar with the relevant end surface of thesection 2. The section 1 has a length of about 5.5 inches, an outsidediameter of 2.0 inches and an internal diameter of 1.875 inches. Thesection 2 has a length of 1.125 inches and an internal diameter of 0.787inch; over most of its length the outside diameter of the section 2 is1.0 inch, but over a length of 0.25 inch extending from the end remotefrom the section 1 this is reduced to 0.95 inch. The length of thesection 2 extending beyond the end of the section 1 is 0.875 inch, andthe section 2 has formed on it an external planar flange 4 whose mainface remote from the section 1 is disposed at a distance of 0.328 inchfrom the end of the section 2 remote from the section '1.

The envelope also includes an annular ceramic mem her 5 having a lengthof 0.5 inch, an outside diameter of 3.0 inches and an inside diameter of1.0 inch. The ceramic member 5' and the copper sections 1 and 2 of theenvelope are arranged coaxially lengthwise, one end face of the ceramicmember 5 being sealed to the face of the United States Patent 0copper-ceramic seal.

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flange 4 that is remote from the section 1, so that the end of thesection 2 projects into the ceramic member 5 to a depth of 0.328 inch. Aceramic backing ring 6 is sealed to the other face of the flange 4 torelieve stresses in the After the envelope has been assembled theexternal surface of the ceramic member 5 is glazed.

The section 1 is divided into two compartments 7 and 8 by means of acopper partition 9 extending transversely across the section 1 about twothirds of the way along its length from the section 2. The electrodesystem of the valve is housed within the larger compartment 7 andincludes a thermionic cathode 10, a heater 11 for the cathode 10 and aheat shield 12 partially surrounding the cathode 10, all disposed abouta third of the way along the compartment '7 from the partition 9. Theelectrode system further includes an anode 13 disposed at the other endof the compartment 7, and between the cathode 10 and the anode 13, inthe order stated, a first baflle 14, a control electrode 15 and a secondbaflle 16. The cathode 10 and one end of the heater 11 are electricallyconnected to the copper portion of the envelope, and the other end ofthe heater 11 is connected to a lead 17 which passes through thepartition 9 and the smaller compartment 8, and is sealed through acircular copper plate 18 which is sealed into the end of the section 1,the lead 17 being insulated from the copper portion of the envelope.

The compartment 8 houses a replenisher 19 for the gas filling of thevalve, the replenisher 19 including a heater 20 which is arranged to besupplied with electric current from the same source as the cathodeheater 11.

The control electrode 15 is provided with a lead 21 in the form of anickel rod which is sealed in an'insulated manner through the curvedportion of the wall of the compartment 7 in the region of the controlelectrode 15.

The baflle 16 is secured to the inside of the section 1 r and the baflle14 is supported on the end of a short copper rod 22 which extendsbetween the baflles 14 and 16 via an aperture in the control electrode15. The purpose of the baflfle 14 is to prevent the evaporation ofelectron emissive material from the cathode 10 onto the controlelectrode 15 and to direct the triggering discharge to the edges of thecontrol electrode 15 in operation; the bafiie 16 serves to screen theanode 13 from the cathode 10 while not preventing the passage of adischarge between these two electrodes.

The anode 13 is in the form of a copper disc, of diameter 1.457 inches,disposed perpendicular to the axis of the envelope and spaced a distanceof 0.195 inch from the end surface of the section 2 that is coplanarwith the flange 3. The anode 13 is supported by means of a copper rod'23 of diameter 0.472 inch which also serves as a lead to the anode 13,the rod 23 extending perpendicularly away from the centre of the anode13 coaxially through the section 2 and the ceramic member 5. A furthercopper flange 24, of diameter 2.0 inches, is sealed around the rod 23and is sealed adjacent its periphery to the second end face of theceramic member 5 thus serving to close the aperture in the ceramicmember 5. At the centre of the face of the flange 24 adjacent theceramic member 5 there is formed a circular recess 25 of diameter 1.625inches and depth 0.025 inch; the flange 24 is, therefore, in contactwith the ceramic member 5 only over an annular surface of internaldiameter 1.625 inches and external diameter 2.0 inches. A ceramicbacking ring 26 whose purpose is to relieve the stresses in the sealbetween the flange 24 and the ceramic member 5 is sealed to the surfaceof the flange 24 remote from the ceramic member 5.

It will be apparent from the dimensions given above that the shortestpath Within the envelope between the flange 24 and the section 2 via thegas-filling is 0.197 inch long. Since the flange 24 and the section 2are respectively at the anode and cathode potentials in operation, thelength of this path cannot be appreciably increased without incurring arisk of the occurrence of a breakdown between these two members via apath through the gasfilling. Breakdown between the flange 24 and thesection 2 may also occur in operation along a path over the surface ofthe ceramic between these two members unless the shortest such path isarranged to be considerably longer than 0.197 inch. This is achieved inthe valve described above by the provision of the recess 25 and by thereduction in outside diameter at the end of the section 2 adjacent theceramic member 5; this results in the flange 24 and the section 2overlapping the ceramic member 5 without touching it by 0.308 inch and0.250 inch respectively so that the shortest path within the envelopebetween the flange 24 and the section 2 along the surface of the ceramicis approximately 0.730 inch long.

Prevention of breakdown between the flange 24 and the section 2 along apath over the external surface of the ceramic member 5 is assisted bythe glazing on the external surface of the ceramic member 5.

A further feature of the valve described, by way of example, is that theceramic member 5 is well removed from the path of the discharge whichoccurs between the anode 13 and the cathode in operation; thismaterially reduces the possibility of sputtering causing a reduction ofthe surface resistance of the inner surface of the ceramic member 5.

We claim: 1

1. A gas-filled electric discharge device comprising an electrodesystem, a sealed gas-filled envelope within which the electrode systemis mounted, said envelope including an elongated hollow generallymetallic structure, a closure member sealing one end of said structure,an annular ceramic member sealed to the other end of said structure, anda metallic closure member sealed to the ceramic member so as to closethe aperture in the ceramic mem ber, the electrode system including atleast an anode and a cathode and being disposed within said hollowstructure so that the main discharge path between the electrodes of saidsystem lies on the side of the anode remote from the ceramic member, theanode being electrically connected to said metallic closure member andelectrically insulated from said hollow structure, and part of at leastone of said metallic closure member and said hollow structureoverlapping the ceramic member without touching it so that the length ofthe shortest path within the envelope between said metallic closuremember and said hollow structure along the surface of the ceramic memberis relatively long compared with the shortest path within the envelopebetween said metallic closure member and said structure via the gasfilling, at least part of the overlap being between the internal surfaceof the ceramic member and the surface of a portion of one of saidmetallic closure member and said hollow structure which portion projectspart way through the aperture in the ceramic member.

2. A device according to claim 1 wherein the end of the ceramic memberadjacent said hollow structure is sealed to one face of an externalplanar flange formed on said hollow structure at a position such thatone end of said hollow structure projects into the aperture in saidceramic member, at least a part of the portion of said hollow structuredisposed within the aperture in said ceramic member overlapping theceramic member without touching it.

3. A device according to claim 1 wherein said hollow structure comprisesa first relatively wide tubular metal section and a second relativelynarrow tubular metal section which is disposed coaxial with and extendsbeyond one end of the first section, the ceramic member being sealed tothe second section so as to be disposed coaxially lengthwise withrespect to said first and second sections, the electrode system beingdisposed within said first section, said metallic closure member beingconstituted by a metal flange sealed to the ceramic member and theelectrical connection between the anode and said metallic closure memberbeing in the form of a metal rod which extends coaxially through thesecond section and the ceramic member and is joined to said flange.

4. A gas-filled electric discharge device comprising an electrodesystem, a sealed gas-filled envelope within which the electrode systemis mounted, said envelope including an elongated hollow generallymetallic structure, a closure member sealing one end of said structure,an annular ceramic member sealed to the other end of said structure, anda metallic closure member sealed to the ceramic member so as to closethe aperture in the ceramic member, the electrode system including atleast an anode and a cathode and being disposed within said hollowstructure so that the main discharge path between the electrodes of saidsystem lies on the side of the anode remote from the ceramic member, theanode being electrically connected to said metallic closure member andelectrically insulated from said hollow structure, and part of at leastone of said metallic closure member and said hollow structureoverlapping the ceramic member without touching it so that the length ofthe shortest path within the envelope between said metallic closuremember and said hollow structure along the surface of the ceramic memberis relatively long compared with the shortest path within the envelopebetween said metallic closure member and said structure via the gasfilling, at least part of the overlap being between the internal surfaceof the ceramic member and the surface of a portion of said hollowstructure which portion projects part way through the .sealed to the endof the ceramic member remote from the hollow structure, said planar facehaving formed in it a recess so that a part of said face overlaps theceramic member without touching it.

References Cited in the file of this patent UNITED STATES PATENTS HullNov. 28, 1944 Clark Oct. 31, 1950

1. A GAS-FILLED ELECTRIC DISCHARGE DEVICE COMPRISING AN ELECTRODESYSTEM, A SEALED GAS-FILLED ENVELOPE WITHIN WHICH THE ELECTRODE SYSTEMIS MOUNTED, SAID ENVELOPE INCLUDING AN ELONGATED HOLLOW GENERALLYMETALLIC STRUCTURE, A CLOSURE MEMBER SEALING ONE END OF SAID STRUCTURE,AN ANNULAR CERAMIC MEMBER SEALED TO THE OTHER END OF SAID STRUCTURE, ANDA METALLIC CLOSURE MEMBER SEALED TO THE CERAMIC MEMBER SO AS TO CLOSETHE APERTURE IN THE CERAMIC MEMBER, THE ELECTRODE SYSTEM INCLUDING ATLEAST AN ANODE AND A CATHODE AND BEING DISPOSED WITHIN SAID HOLLOWSTRUCTURE SO THAT THE MAIN DISCHARGE PATH BETWEEN THE ELECTRODES OF SAIDSYSTEM LIES ON THE SIDE OF THE ANODE REMOTE FROM THE CERAMIC MEMBER, THEANODE BEING ELECTRICALLY CONNECTED TO SAID METALLIC CLOSURE MEMBER ANDELECTRICALLY INSULATED FROM SAID HOLLOW STRUCTURE, AND PART OF AT LEASTONE OF SAID METALLIC CLOSURE MEMBER AND SAID HOLLOW STRUCTUREOVERLAPPING THE CERAMIC MEMBER WITHOUT TOUCHING IT SO THAT THE LENGTH OFTHE SHORTEST PATH WITHIN THE ENVELOPE BETWEEN SAID METALLIC CLOSUREMEMBER AND SAID HOLLOW STRUCTURE ALONG THE SURFACE OF THE CERAMIC MEMBERIS RELATIVELY LONG COMPARED WITH THE SHORTEST PATH WITHIN THE ENVELOPEBETWEEN SAID METALLIC CLOSURE MEMBER AND SAID STRUCTURE VIA THE GASFILLING, AT LEAST PART OF THE OVERLAP BEING BETWEEN THE INTERNAL SURFACEOF THE CERAMIC MEMBER AND THE SURFACE OF A PORTION OF ONE OF SAIDMETALLIC CLOSURE MEMBER AND SAID HOLLOW STRUCTURE WHICH PORTION PROJECTSPART WAY THROUGH THE APERTURE IN THE CERAMIC MEMBER.